1. Field of the Invention
The present invention relates to pipe joints and flange joints, and more particularly, to a gasket deformation indicator for improving maintenance of a pipe joint or flange joint.
2. Description of the Background
Flanges are commonly used in joints for conduits, vessels, rotating equipment and the like, including pipes, valves and heat exchangers. One function of a flange is to provide a leak-free joint seal. A typical flange assembly comprises two flange elements, packing material positioned between the flange elements to provide a seal, and fasteners passing into or through the flange elements for urging the flange elements against the packing material to form the leak-free seal.
Packing material useful in flanges is generally of a resilient, compressible material that deforms against the flange elements when compressive force is applied, by the flange elements against the packing material. The compressive force is generally applied by the fasteners, often through the medium of one or more spring devices mounted on the fasteners. When the compressive force is reduced or removed, the packing material, at least to some extent, recovers its original or previous shape. However, over time and with repeated deformations, the packing material loses resiliency and becomes permanently deformed in a process known as "creep". Creep of the packing material may compromise the seal in the joint, leading to leaks in the joint; to compensate, the fasteners clamping the flange elements must be periodically readjusted to restore the compressive force on the packing material and thus reseal the joint.
One or more spring devices may be installed in the flange assembly, usually mounted on the fasteners, to help maintain a "live-load" on the packing material. While these spring devices are generally adequate for maintaining a stable seal over the life of packing material subjected to only mild conditions of temperature and pressure, packing material subjected to severe conditions and/or to thermal cycling will often undergo excessive creep beyond what can be accommodated by the spring devices to maintain adequate compressive force. Under these conditions the fasteners on the flange assembly is frequently adjusted to maintain a leak-free seal.
Adjusting each fastener to achieve a leak-free joint must be done with great care. Undertightening the fasteners results in an inadequate seal. Overtightening the fasteners may damage the integrity of the packing material. It is desirable to have available an indicator for indicating the extent of deformation of the packing material in a flange assembly. Desirably, such an indicator would provide reproducible measurement of the extent of deformation without requiring that the flange assembly be disassembled in order to make the measurement. While a number of devices have been disclosed for indicating the tension on a fastener (Examples include U.S. Pat. Nos. 3,823,639; 4,020,734; 4,131,050, 4,293,257; 4,479,747; 4,500,237; 4,572,717; 4,773,272; 4,930,951; 5,195,756; 5,199,835.), all are inadequate for maintaining a seal in a flange assembly and for achieving a predetermined amount of deformation of the packing material contained in the flange assembly.